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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>12.6 Local Binding with Splicing Body</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Reference</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewselflink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18 </td><td><a href="runni
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<span class="RktSym"><a href="let.html#%28form._%28%28quote._~23~25kernel%29._letrec-values%29%29" class="RktStxLink" data-pltdoc="x">letrec-values</a></span>, <span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let-syntax%29%29" class="RktStxLink" data-pltdoc="x">let-syntax</a></span>, <span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._letrec-syntax%29%29" class="RktStxLink" data-pltdoc="x">letrec-syntax</a></span>,
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<span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let-syntaxes%29%29" class="RktStxLink" data-pltdoc="x">let-syntaxes</a></span>, <span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._letrec-syntaxes%29%29" class="RktStxLink" data-pltdoc="x">letrec-syntaxes</a></span>,
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<span class="RktSym"><a href="let.html#%28form._%28%28quote._~23~25kernel%29._letrec-syntaxes%2Bvalues%29%29" class="RktStxLink" data-pltdoc="x">letrec-syntaxes+values</a></span>, <span class="RktSym"><a href="local.html#%28form._%28%28lib._racket%2Flocal..rkt%29._local%29%29" class="RktStxLink" data-pltdoc="x">local</a></span>, and
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<span class="RktSym"><a href="parameters.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._parameterize%29%29" class="RktStxLink" data-pltdoc="x">parameterize</a></span>, except that in a definition context, the body
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forms are spliced into the enclosing definition context (in the same
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way as for <span class="RktSym"><a href="begin.html#%28form._%28%28quote._~23~25kernel%29._begin%29%29" class="RktStxLink" data-pltdoc="x">begin</a></span>).</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-let-syntax%29%29" class="RktStxLink" data-pltdoc="x">splicing-let-syntax</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">one</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">o</span><span class="hspace"> </span><span class="RktSym">one</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktSym">o</span></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktSym">one</span></td></tr><tr><td><p><span class="RktErr">one: undefined;</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">cannot reference an identifier before its definition</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in module: top-level</span></p></td></tr></table></blockquote></div></p><p>When a splicing binding form occurs in a <a href="syntax-model.html#%28tech._top._level._context%29" class="techoutside" data-pltdoc="x"><span class="techinside">top-level context</span></a> or
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<a href="syntax-model.html#%28tech._module._context%29" class="techoutside" data-pltdoc="x"><span class="techinside">module context</span></a>, its local bindings are treated similarly to
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definitions. In particular, syntax bindings are
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evaluated every time the module is <a href="syntax-model.html#%28tech._visit%29" class="techoutside" data-pltdoc="x"><span class="techinside">visit</span></a>ed, instead of only
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once during compilation as in <span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let-syntax%29%29" class="RktStxLink" data-pltdoc="x">let-syntax</a></span>, etc.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-letrec%29%29" class="RktStxLink" data-pltdoc="x">splicing-letrec</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">x</span><span class="hspace"> </span><span class="RktSym">bad</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">bad</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">bad.1: undefined;</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">cannot reference an identifier before its definition</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in module: top-level</span></p></td></tr></table></blockquote></div></p><p>If a definition within a splicing form is intended to be local to the
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splicing body, then the identifier should have a true value for the
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<span class="RktVal">'</span><span class="RktVal">definition-intended-as-local</span> <a href="stxprops.html#%28tech._syntax._property%29" class="techoutside" data-pltdoc="x"><span class="techinside">syntax property</span></a>. For
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example, <span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-let%29%29" class="RktStxLink" data-pltdoc="x">splicing-let</a></span> itself adds the property to
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locally-bound identifiers as it expands to a sequence of definitions,
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so that nesting <span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-let%29%29" class="RktStxLink" data-pltdoc="x">splicing-let</a></span> within a splicing form works as
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expected (without any ambiguous bindings).</p><p class="SHistory">Changed in version 6.12.0.2 of package <span class="stt">base</span>: Added <span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-parameterize%29%29" class="RktStxLink" data-pltdoc="x">splicing-parameterize</a></span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><a name="(form._((lib._racket/splicing..rkt)._splicing-syntax-parameterize))"></a><span title="Provided from: racket/splicing | Package: base"><span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-syntax-parameterize%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">splicing-syntax-parameterize</a></span></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="stxparam.html#%28form._%28%28lib._racket%2Fstxparam..rkt%29._syntax-parameterize%29%29" class="RktStxLink" data-pltdoc="x">syntax-parameterize</a></span>, except that in a definition context, the body
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forms are spliced into the enclosing definition context (in the same way as for
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<span class="RktSym"><a href="begin.html#%28form._%28%28quote._~23~25kernel%29._begin%29%29" class="RktStxLink" data-pltdoc="x">begin</a></span>). In a definition context, the body of
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<span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-syntax-parameterize%29%29" class="RktStxLink" data-pltdoc="x">splicing-syntax-parameterize</a></span> can be empty.</div></p><p>Note that <a href="stxtrans.html#%28tech._require._transformer%29" class="techoutside" data-pltdoc="x"><span class="techinside">require transformers</span></a> and <a href="stxtrans.html#%28tech._provide._transformer%29" class="techoutside" data-pltdoc="x"><span class="techinside">provide transformers</span></a> are not
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affected by syntax parameterization. While all uses of <span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span> and
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<span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._provide%29%29" class="RktStxLink" data-pltdoc="x">provide</a></span> will be spliced into the enclosing context, derived import or
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export specifications will expand as if they had not been inside of the
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<span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-syntax-parameterize%29%29" class="RktStxLink" data-pltdoc="x">splicing-syntax-parameterize</a></span>.</p><p>Additionally, <a href="eval-model.html#%28tech._submodule%29" class="techoutside" data-pltdoc="x"><span class="techinside">submodules</span></a> defined with <span class="RktSym"><a href="module.html#%28form._%28%28quote._~23~25kernel%29._module%2A%29%29" class="RktStxLink" data-pltdoc="x">module*</a></span> that specify
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<span class="RktVal">#f</span> in place of a <a href="Module_Names_and_Loading.html#%28tech._module._path%29" class="techoutside" data-pltdoc="x"><span class="techinside">module path</span></a> <span class="emph">are</span> affected by syntax
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parameterization, but other submodules (those defined with <span class="RktSym"><a href="module.html#%28form._%28%28quote._~23~25kernel%29._module%29%29" class="RktStxLink" data-pltdoc="x">module</a></span> or
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<span class="RktSym"><a href="module.html#%28form._%28%28quote._~23~25kernel%29._module%2A%29%29" class="RktStxLink" data-pltdoc="x">module*</a></span> with a <a href="Module_Names_and_Loading.html#%28tech._module._path%29" class="techoutside" data-pltdoc="x"><span class="techinside">module path</span></a>) are <span class="emph">not</span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="stxparam.html#%28form._%28%28lib._racket%2Fstxparam..rkt%29._define-syntax-parameter%29%29" class="RktStxLink" data-pltdoc="x">define-syntax-parameter</a></span><span class="hspace"> </span><span class="RktSym"><a href="places.html#%28form._%28%28lib._racket%2Fplace..rkt%29._place%29%29" class="RktStxLink" data-pltdoc="x">place</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktVal">"Kansas"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._define-syntax-rule%29%29" class="RktStxLink" data-pltdoc="x">define-syntax-rule</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">where</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">`</span><span class="RktVal">(</span><span class="RktVal">at</span><span class="hspace"> </span><span class="RktRdr">,</span><span class="RktPn">(</span><span class="RktSym"><a href="places.html#%28form._%28%28lib._racket%2Fplace..rkt%29._place%29%29" class="RktStxLink" data-pltdoc="x">place</a></span><span class="RktPn">)</span><span class="RktVal">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">where</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'(at "Kansas")</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="splicing.html#%28form._%28%28lib._racket%2Fsplicing..rkt%29._splicing-syntax-parameterize%29%29" class="RktStxLink" data-pltdoc="x">splicing-syntax-parameterize</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym"><a href="places.html#%28form._%28%28lib._racket%2Fplace..rkt%29._place%29%29" class="RktStxLink" data-pltdoc="x">place</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktVal">"Oz"</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">here</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">where</span><span class="RktPn">)</span><span class="RktPn">)</span><span cl
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specify <span class="RktVal">#f</span> in place of a <a href="Module_Names_and_Loading.html#%28tech._module._path%29" class="techoutside" data-pltdoc="x"><span class="techinside">module path</span></a>.</p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="stxparam.html" title="backward to "12.5 Syntax Parameters"" data-pltdoc="x">← prev</a> <a href="Macros.html" title="up to "12 Macros"" data-pltdoc="x">up</a> <a href="stxprops.html" title="forward to "12.7 Syntax Object Properties"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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